Emission factors of mercury and particulate matters, and in situ control of mercury during the co-combustion of anthracite and dried sawdust sludge

Anthracite and dried sawdust sludge (DSS) were demonstrated as a complementary combination. Since air pollution has attracted great concern, this paper studies the emission characteristics of mercury and particulate matters (PMs) during the co-combustion process. The results indicated that no Hg2+ was produced in all cases. The Hg-0 emission factor decreased significantly with the increasing of DSS. The rising temperature from 800 to 900 degrees C slightly promoted the Hg-0 emission, but the further increasing temperature caused a decreasing of Hg-0 emission. Oxygen-enrich atmosphere accelerated the release of Hg-0 from anthracite, but the DSS combustion was independent on the atmospheric conditions. The emission factor of PMs for DSS was 10.5 +/- 1.7 mg/kg which was 9 times higher than that of anthracite combustion (95.2 +/- 7.7 mg/kg). The results of in situ control of Hg-0 demonstrated the co-combustion of fuel and Ca-based additives could not deeply reduce Hg-0 emission, however the integrated approach of gas phase oxidation combined with wet absorption was satisfactory in terms of Hg-0 control, and the way of post-combustion injection was better, the oxidation efficiencies of Hg-0 reached 62.5%. The main existing forms of mercury were determined as HgSO4 and HgX2 (X: Br or Cl) by XPS, the reaction mechanism of Hg-0 removal was proposed accordingly.